It's no relation to the mob at all*, but instead of the buffs received. You don't describe the mob as 'high defense' because really every weapon of a type should have the roughly the same STR and Attack, so the mob has the same relative defenses to any of them. What differs is two things: Delay, and Hitbuild. By this I mean final Round Delay after Haste, Dual Wield, etc, and Hitbuild as in Effective Hitbuild and is excluding the WS hit.
*Execpt when it has less HP than your WS deals, but that's an efficiency concept I've yet to pen an editorial on.
Round Delay and Effective Hitbuild (EHB) are very specific concepts that are the difference between a Vanilla weapon and a Multihit weapon within my sphere of concepts. What it boils down to is: A low EHB is actually damaged in effectiveness by a reduction in Round Delay. The lower your EHB, the more your Round Delay results in you eating more WS delay.
A 2-4 or OAT weapon serves to reduce EHB directly without affecting or really requiring a reduction in Round Delay. Multi-Attack Traits and Gear serve the same purpose, albeit smaller reductions due to probabilistic influences.
Additions of Haste, Dual Wield, or Martial Arts serve to reduce Round Delay.
What this boils down to:
EHB * Round Time + 120 WS delay = Cycle time
What happens is the ratio of your 120 seconds of WS time delay to your EHB * Round Time gets smaller and smaller but can only ever approach 120 Delay (two seconds). It's a mathematical limit; oh the rant's I've dropped about the difference between a 'cap' and a 'limit' in this context. When fSTR, Attack, and Accuracy are capped, you then increase damage by decreasing Cycle Time per the factors of Round Time and EHB.
What Multihit weapons do, OAT and 2-4, is trade a portion of their Base Damage for a reduction in Effective Hit Build. They're already playing this game of reducing Cycle Time to increase damage at the minimalized penalty of Base Damage due to the high WSC of Resolution or Entropy. Exactly in the vein of stacking Double Attack, this game can only go so far (approaching the flat WS Delay value of 120). It's a 'diminishing returns' concept: the more you reduce EHB and Round Delay, the less effective doing so is because it has a valued Limit.
You probably already understand this concept as 'WS Saturation', but there's more to it.
The EHB of a 5-hit 2-4 weapon is something like 2.63. Naturally you can't be WSing after '2.63 rounds exactly', this comes from a probabilistic set of completing a cycle in 1, 2, 3, or 4 hits when 5-hitting. A vanilla weapon 5-hitting with no multiattack traits or gear has an EHB of 4.0, naturally, this means that 2-4 is a 34.25% reduction (1 - 2.63 / 4) in EHB over a Vanilla weapon, but this does not correlate directly to WS rate due to WS Delay. Instead you get
528 * 2.63 + 120 = 1508 delay
528 * 4 + 120 = 2232 delay
1 - 1508 / 2760 = 32.4% reduction in cycle time from EHB.with zero haste.
Now is when the problem starts. Let's just throw DRK's native 50% haste at both.
264 * 2.63 + 120 = 814 delay
264 * 4 + 120 = 1176 delay
1 - 814 / 1440 = The cycle time decrease from EHB is only a 30.8% reduction in cycle time.
And the extreme, capped 80% haste:
105.6 * 2.63 + 120 = 398 delay
105.6 * 4 + 120 = 542 delay
1 - 398 / 648 = EHB now only contributes a 26.6% reduction in cycle time.
So from 0% to 50% haste, 2-4's EHB effect on cycle time loses only about 5% of it's effectiveness, but from 50% to 80% loses another 14% to about 18% just being wasted. The problem therein is you're now spending 30% of your time WSing and hardly have time to swap gear (I can attest to this).
Now let's say you have +45 Save TP from Discipline and COR (I wasn't looking forward to this part when I started this diatribe). This was much worse when it stacked with your WS return, literally anything had a 2-hit build,
Excuse me while I recalculate EHB of 2-4 (40/30/20/10 distribution)...
1 round - 0.3 (4 hits or 3 hits)
3 rounds - .4 * .4 = 0.16 (can only be with two consecutive singles)
2 rounds - Difference of 0.54 (easy way to work out single->double and double->single permutations)
1.86 EHB, 4-hit (or +45 Save TP) 2-4 weapon. Notice it's nothing like 2.63 - 1.
50% native haste:
264 * 1.86 + 120 = 611 delay
264 * 3 + 120 = 912 delay
1 - 611 / 912 = 33% reduction in cycle time from EHB. You can already see where high buffs are starting to hurt.
80% capped haste:
105.6 * 1.86 + 120 = 316 delay
105.6 * 3 + 120 = 437 delay
1 - 316 / 437 = 2-4's superior EHB is now only a measly 27.7% reduction in Cycle Time.
All told, with the the native 50% haste, a 30.8% reduction in cycle time from EHB results in 44.5% more Weaponskills (1 / (1 - 0.308)). Get full Voidwatch buffs and you're now only getting 38.3% (1 - (1 - 0.277)) more WSes, 15% less 'gain'.
That is actually a big-*** change, because consider that 70%-80% of the 2-4's damage is going to be from WSing. It actually loses 10.5%-12% (0.15 * 0.7 to 0.8) of it's total damage output automatically from gaining buffs! (Yes, that is the post-buffs damage that is being affected by that amount, I had to chew on the concept for about an hour to be sure)
That is why bringing a 2-4 weapon to 'hard' mobs is a bad idea: Interaction of extreme buffs with the advantage of a multihit weapon It has nothing to do with the mob being attacked, but the buffs received! It is incredibly detrimental to 2-4's advantages to so greatly reduce Cycle Time with other EHB reductions or reductions in Round Delay, let alone both at once as with Voidwatch buffs.
So again, it has nothing to do with the mob, but buffs garnered via the event and situation.
____________________________I've seen things you people wouldn't believe. Airships on fire off the shoulder of Bahamut. I watched Scapula Beams glitter in the dark near the Three Mage Gate...
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